Magnetic Polarity of Upper Triassic Sediments of the Germanic Basin in Poland

Annales Societatis Geologorum Poloniae (2015), vol. 85: 663–674. doi: http://dx.doi.org/10.14241/asgp.2015.026

MAGNETIC POLARITY OF UPPER TRIASSIC SEDIMENTS OF THE GERMANIC BASIN IN POLAND

Jerzy NAWROCKI 1, Karol JEWU£A2, Aleksandra STACHOWSKA3 & Joachim SZULC2

1 Polish Geological Institute – NRI, Rakowiecka 4, PL- 00-975 Warszawa, Poland; e-mail: [email protected] 2 Institute of Geological Sciences, Jagiellonian University, Oleandry 2a, PL-30-063 Kraków, Poland; e-mails: [email protected]; [email protected] 3 Faculty of Geology, University of Warsaw, al. ¯wirki i Wigury 93, PL-02-089 Warszawa, Poland; e-mail: [email protected]

Nawrocki, J., Jewu³a, K., Stachowska, A. & Szulc, J., 2015. Magnetic polarity of Upper Triassic sediments of the Germanic Basin in Poland. Annales Societatis Geologorum Poloniae, 85: 663–674.

Abstract: Palaeomagnetic results are presented for 205 samples of cores from the Ksi¹¿ Wielkopolski IG-2, WoŸniki K1 and Patoka 1 wells, drilled in the Polish part of Germanic Basin. The magnetic polarity stratigraphy is based on the inclination of the characteristic remanent magnetization, isolated in 60% of the total samples and found to be in general agreement with the expected Late Triassic inclination at the sampling sites. A total of 22 magnetozones from the integration of the three records correspond to about 25% of the published polarity zones for the Upper Triassic sediments that were combined in the worldwide composite polarity-time scale. The magnetic polarity pattern, defined for the Schilfsanstein, fits very well with the one defined in the Tethys area for the upper part of the Julian sub-stage. According to the magnetostratigraphic data, the uppermost part of the Upper Gypsum Beds (equivalent to the Ozimek Member of the redefined Grabowa Formation) and the lowermost part of the Patoka Member, containing the Krasiejów bone-breccia horizon, can be correlated with the latest Tuvalian (~228.5 Ma) or with the middle part of Lacian (~225 Ma). However, if the “Long-Tuvalian” option for the Late Triassic Time Scale is taken into consideration, the parts of these substages mentioned above should be correlated with ~221.5 Ma and ~218.5 Ma, respectively.

Key words: Magnetostratigraphy, Grabowa Formation, Upper Triassic, Germanic Basin, Poland.

Manuscript received 27 January 2015, accepted 8 July 2015

INTRODUCTION The lithofacies of the Upper Triassic (Keuper) strati- stratigraphy provides the only means of improving regional graphic succession of the Germanic basin, including its Pol- and global correlation of the Keuper succession. In the bio- ish part, reflect alternating shallow-marine and continental stratigraphy of the Germanic Keuper, the main tool enabling environments and fluctuations between arid and humid cli- chronostratigraphic correlation is palynostratigraphy. For matic conditions. The layer-cake lithostratigraphy is broa- the purpose of this paper, it is important to note the most im- dly uniform throughout the basin; it resulted from the inter- portant and accurate palaeobotanical data supporting the ac- play between eustatic and climatic fluctuations, overwhelm- curacy of the magnetostratigraphical correlation. This con- ing the entire Western Tethys domain during Carnian– cerns in particular the Schilfsandstein (Stuttgart Fm), pre- Rhaetian time. This created a sequence-stratigraphic frame- cisely dated as Julian by means of both palynonomorphs work linking the well established bio- and chronostratigra- (Or³owska-Zwoliñska, 1985; Fija³kowska-Mader et al., phy of the Alpine Upper Triassic records with its Germanic 2015) and megaspores (Wierer, 1997). On the other hand, equivalent, which is without age-diagnostic fossils (Szulc, very careful and detailed study applying lithofacies exami- 2000). Also the regional extent of climatic variation (arid nation, palaeozoological and palynological analyses and se- vs. pluvial conditions) supported the reliable correlation of quence-stratigraphy procedures unequivocally indicates a the main Upper Triassic lithostratigraphic units with their late Fassanian–Longobardian age of the Lower Keuper suc- Alpine time equivalents (Feist-Burkhardt et al., 2008). cession including the Grenzdolomit interval (Or³owska-Zwo- Nonetheless, the scarcity of age-diagnostic fossils, limited liñska, 1985, Szulc, 2000, Narkiewicz and Szulc, 2005) and to only a few units (see below), impedes more detailed bio- Franz et al. (2015). and chronostratigraphic study, with the result that magneto- 664 J. NAWROCKI ET AL.

Fig. 1. The cores selected for palaeomagnetic investigation. A. Location of the cores studied on a sketch map of the distribution of the Upper Triassic sediments in Poland (after Fig. 52 in Deczkowski, 1997). B. Lithostratigraphy of the Upper Triassic deposits from the Ksi¹¿ Wielkopolski, WoŸniki K1 and Patoka 1 cores.

The Late Triassic magnetic polarity scale has been de- with that found in the upper part of the Newark Supergroup veloped in marine and nonmarine sections. The Late Trias- succession (Hounslow et al., 2004). Results of magnetostra- sic deposits of the Newark Basin allowed to reconstruct a tigraphic correlation of Tethyan sections with the succes- cycle-scaled record of magnetic reversals in which the top sions of the Newark basin reveal that the base of Rhaetian is of the youngest magnetozone E24 is as old as 202 Ma (Kent placed between chrons E16n and E16r (Hüsing et al., 2011). et al., 1995; Kent and Olsen, 1999). This mixed magnetic Gradstein et al. (2012) have presented the calibration of po- polarity behaviour is characterized by quite long normal or larity patterns in relation to ammonite zones defined in reversed magnetozones alternating with short-lived ones. magnetostratigraphy reference successions (Hounslow and Magnetostratigraphic correlation between the terrestrial Muttoni, 2010) where the ammonite zonal boundaries were Newark polarity scale and biostratigraphically calibrated adjusted to the Newark magnetic polarity scale. The Julian scales from the Ladinian through Rhaetian marine sections part of this synthetic scale was constructed according to the from the Alpine area is difficult because of different sedi- data obtained from the reference sections in the Alpine area mentation rates and tectonic deformations (Krystyn et al., and Turkey (Gallet et al., 1992, 1998). The upper Carnian 2002; Channell et al., 2003). On the other hand the mag- through Norian slice was mostly constructed by the means netostratigraphy of terrestrial to shallow-water sediments of the data from the locality at Pizzo Mondello in Sicily from the St. Audrie’s Bay section in the UK matches well (Muttoni et al., 2004) and the Silická Berezová succession MAGNETIC POLARITY OF UPPER TRIASSIC SEDIMENTS 665

of Slovakia (Channel et al., 2003). The uppermost Norian to lowermost Rhaetian interval was correlated with conodont zones defined in Austrian sections (Gallet et al., 1998; Krystyn et al., 2007; Hüsing et al., 2011). The middle Rhaetian through lowermost Hettangian part of the scaled polarity pattern was derived from the southern Alps (Mut- toni et al., 2010). Because of the deficiency of adequate correlation markers, Gradstein et al. (2012) presented two alternative versions of the Late Triassic magnetic polarity scale. According to a concept with a long-duration Tuvalian substage and presence of the Rhaetian gap in the Newark scale, the Late Triassic is subdivided into ~16-myr long Carnian and Norian of the same duration. The Rhaetian covers a 4 myr time span only. In the option with short-lasting Carnian and occurrence of Rhaetian in the Newark scale, the Late Triassic is subdivided into 8 myr long Rhaetian and 19 myr long Norian. In this model the Carnian Stage covers ~10 myr time span. The Schilfsanstein of Western Europe sections was palaeomagnetically studied by Hahn (1984). The older part of this unit, sampled in the Weserbergland and Franken, displayed normal magnetization only. On the other hand, its younger part sampled in the Schwaben and N. Switzerland was magnetized in the reverse direction. Unfortunately, the samples studied were not linked with any geological pro- files. Therefore, the possibility cannot be excluded that the Fig. 2. Formal and informal lithostratigraphic units of the Up- two magnetozones distinguished there cover only a small per Triassic in Upper Silesia. After fig. 2 in Szulc and Racki part of the Schilfsanstein. (2015), modified. In this paper the authors present preliminary magnetostratigraphic data on the Upper Triassic sediments of the tire Germanic Basin. The overlying interval, represented Germanic Basin in Poland, in its central and marginal (Up- mainly by grey mudstones and claystones with anhydrite in- per Silesian) parts. Poor biostratigraphic documentation, tercalations, corresponds to the Lower Gypsum Beds. These stratigraphic frames that correspond mainly to lithological pass into the Schilfsandstein, which mainly consists of grey and environmental lines of evidence, and gaps in sedimenta- mudstones and sandstones with some coal seams. The grey tion (e.g., Szulc et al., 2015) do not favour these rocks as sandstones and mudstones pass gradually into reddish mud- very promising ones for regional magnetostratigraphic cor- stones with traces of roots. The Schilfsanstein is overlain by relation. On the other hand, the succession contains red beds the Upper Gypsum Beds, included as the Ozimek Member that provide a reliable primary palaeomagnetic signal, in the revised Grabowa Variegated Mudstone-Carbonate which also has been recognized in the underlying Buntsand- Formation (Szulc and Racki, 2015; Szulc et al., 2015; Fig. 2), stein sediments of the same basin (e.g., Nawrocki, 1997). developed as monotonous, multicoloured mudstones, containing gypsum intercalations and nodules. Above that, the Steinmergelkeuper can be distinguished. It consists mainly DRILL CORES STUDIED of variegated mudstones and claystones without gypsum intercalations. The thin horizons of vadose conglomerates, For the present study, drill cores from the Ksi¹¿ Wiel- palaeosoils and beds with regolith are characteristic for this kopolski IG-2 (approximately 1,000 m long), WoŸniki K1 interval. The Steinmergelkeuper interval recently was defi- (100 m) and Patoka 1 (208 m) boreholes were sampled ned for southern Polish Keuper lithostratigraphy as the Pa- (Fig. 1). The drill core from the Ksi¹¿ Wielkopolski IG-2 toka Mudstone-Sandstone Member of the Grabowa Forma- well contains very distinct Keuper horizons, starting from the tion (Szulc and Racki, 2015; Szulc et al., 2015; Fig. 2). Grenzdolomite and ending with the Upper Gypsum Beds. The core from the Patoka 1 well comprises a sedimen- The Lower Gypsum Beds include about 60 m of salt. The tary succession, assigned to the Grabowa Formation (Upper Schilfsanstein (about 60 m thick) consists of sandstones, Gypsum Beds, Steinmergelkeuper) and the uppermost Tri- mudstones and siltstones in its upper part. The Upper Gyp- assic – lowermost Jurassic clastic sediments (“Po³omia For- sum Beds terminate with an anhydrite horizon. A monoto- mation”). In contrast to the core from the WoŸniki K-1 well, nous series of siltstones, claystones and clays about 500 m there is no clear evidence of Schilfsandstein facies. The thick belong to the Norian and Rhaetian, which are not sep- Steinmergelkeuper is represented by variegated claystones arated here. and mudstones, as well as grey sandstones with a sharp ero- The WoŸniki K1 drill core begins at the bottom with a sional base. The distinct feature of this succession is the oc- dolomite interval, corresponding to the Grenzdolomite hori- currence of pedogenic horizons, caliche, regoliths, debris zon that is a widely distributed horizon across almost the en- flows and slump structures. The topmost part of the core an- 666 J. NAWROCKI ET AL.

Table 1 of the palaeomagnetic specimens according to their spec- trum of unblocking temperatures. It should be stressed that Summary statistics of characteristic palaeomagnetic in the grey and red beds of the Buntsandstein a mixture of inclinations obtained from the Upper Triassic rocks drilled different ferric oxides was recognized, with hematite as the in the Ksi¹¿ Wielkopolski IG-2,WoŸniki K1 main carrier in the red beds and magnetite and/or maghe- and Patoka 1 wells mite carrying the remanence in the grey-coloured rocks (Nawrocki, 1997). Number of Mean Standard Locality samlpes inclination deviation N I SD Ksi¹¿ Wielki IG-2 RESULTS OF DEMAGNETIZATION – normal polarity 21 44.38 12.15 Ksi¹¿ Wielkopolski IG-2 – reversed polarity 37 –38.59 14.09 – all 58 40.69 13.71 Generally, four types of palaeomagnetic behaviour can WoŸniki K1 be distinguished. Part (~36%) of the samples revealed the – normal polarity 16 33.46 13.29 dominance of one component with unblocking temperatures – reversed polarity 21 –37.41 13.85 – all 37 35.54 13.55 as high as at least 600 °C, and negative or positive inclinations of ~40–50° (Fig. 3, samples k36A and k62a). In these Patoka 1 – normal polarity 23 38.91 12.83 samples, most of the NRM initial intensity was usually lost – reversed polarity 4 –55.25 21.37 during thermal demagnetization at temperatures between – all 27 41.33 15.06 400 and 550 °C. Because of this, it can be assumed that the CHRM is carried here by the hematite and magnetite grains together (e.g., Dunlop and Özdemir, 1997). Another set of alyzed is represented by grey and white conglomerates, and samples (~52%), apart from that portion of the CHRM, was coarse sandstones, which represent the uppermost Triassic. recognized as containing also the unstable low-temperature distinct component that was removed at temperatures not higher than 300 °C (Fig. 3, samples k25d and k30b). This METHODS component is probably of viscous origin and can be linked with the magnetite fraction, susceptible to such a kind of ma- A total of 205 fragments of cores were taken as hand gnetization. Some grey-coloured samples have a similar stru- samples, oriented only with respect to top and bottom. They cture of magnetization, but the most stable dual-polarity com- were cut into a maximum of 6 cubic (8 cm3) or cylindrical ponent was removed at lower temperatures of 470–560 °C (11.3 cm3) standard specimens for palaeomagnetic analysis, (Fig. 3, samples k68c and k41b), which is typical of magne- giving a total of 374 specimens. The clay horizons provided tite. The last set of samples contains a very distinct low-tem- mainly cracked samples, not suitable for the preparation of perature component, often removed at temperatures not specimens. Part (57) of the specimens fell to pieces very higher than 200 °C and probably carried by ferric oxyhydro- quickly in the first stages of laboratory heating. xide (e.g., goethite). A stable dual-polarity component oft- The natural remanent magnetization (NRM) was mea- linewas isolated at a maximum unblocking temperature of sured on JR-5 and JR-6 spinner magnetometers (AGICO close to 400 °C (Fig. 3, sample k45a). Its inclination corre- Ltd.) with a noise level of 5 × 10–5 A/m. A stepwise thermal sponds to the expected late Triassic value. Summary statis- demagnetization with maximum temperatures of up to 700 °C tics for the characteristic inclinations at the sample level are was performed, using a µ-metal shielded oven MMTD1 presented in Table 1. The mean value of this parameter for (Magnetic Measurements Ltd.), which reduced the ambient the entire set of data amounts to 40.69° with a standard de- field to a few nT. After each steep of heating, the magnetic viation of 13.71°. susceptibility was measured, using a KLY-2 susceptibility The magnetic-polarity pattern, reconstructed for the bridge (Geofyzika Brno). Characteristic remanent magneti- core studied, against the background of the line-fit charac- zation (CHRM) directions were calculated by principal teristic directions is very discontinuous (Fig. 4). Gaps occur component analysis (Kirschvink, 1980) using Remasoft in the places not suitable for sampling (e.g., clays destroyed (Chadima and Hrouda, 2006) and PCA (Lewandowski et during coring and core storage, salts) or where the samples al., 1997) software. Late Triassic inclinations of the geo- were destroyed during the initial levels of thermal demagne- magnetic field for the study area calculated from existing tization. Four separate and distant parts of the Upper Trias- data and not corrected for inclination shallowing, should be sic succession provided fragments with a continuous pala- confined to between 39° and 60° (e.g., Torsvik et al., 2012) eomagnetic record. This amounts to about 35% of its total and should differ from the present-day inclination in central thickness. The magnetic polarity of the Lower Keuper strata Poland (67°) by up to 28° for the oldest Lower Keuper is reversed at the bottom and mainly normal in the upper strata. Because of this difference, any geologically recent part. The uppermost part of the Lower Gypsum Beds and magnetic overprint directions should be distinguished, es- the Schilfsanstein were deposited mainly during a time of pecially in the Lower-Middle Keuper part of the sedimen- reversed-polarity geomagnetic field, interrupted by three in- tary sequence studied. tervals of normal polarity (Fig. 4). The lowermost part of Direct studies of magnetic carriers were not performed. the Norian sequence is similar to what was described for the They were recognized during the thermal demagnetization Lower Keuper beds. Three magnetozones with the thickest MAGNETIC POLARITY OF UPPER TRIASSIC SEDIMENTS 667

Fig. 3. Typical demagnetization characteristics (demagnetization paths, intensity decay curves and orthogonal plots) of’ the Upper Triassic samples from the Ksi¹¿ Wielkopolski IG-2 core. Circles in the orthogonal plots represent vertical projections, squares represent horizontal projections. Irm – intensity of remanent magnetization, Inrm – initial intensity of natural remanent magnetization. The diagrams were prepared by the means of a computer package written by Lewandowski et al. (1997). 668 J. NAWROCKI ET AL.

zone of reversed polarity were distinguished in the topmost (i.e. late Rhaetian) part of the section.

WoŸniki K1 Samples from the reddish sandstones and mudstones of the WoŸniki K-1 core usually contain one distinct component carried by hematite, with unblocking temperatures higher than 600 °C (Fig. 5A, samples 1A, 40A, 12C). In some samples, the same component with a shallow negative or positive inclination also is carried by magnetite with unblocking temperatures of ca. 550 °C (Fig. 5A, sample 50A), or by magnetite and hematite together (Fig. 5, sample 16B). In addition, a very unstable low-temperature component of magnetization, carried most probably by the ferric hydro- oxides, is typical for most of samples taken from the clays (Fig. 5A, sample 20A). As might be expected, all directions isolated from samples oriented with respect to top and bottom on the stereonet form only a belt that is azimuthally dispersed and inclinations mainly between 30° and 60° (Fig. 5B). The WoŸniki K1 core contains sediments from the Carnian and Norian stages of the Upper Triassic (see Szulc et al., 2015; Fija³kowska-Mader et al., 2015), but their small thickness and different environments of deposition may indicate a discontinuous character of sedimentation. There are also several breaks in palaeomagnetic sampling and some places without good-quality data. The value of the mean inclination, calculated for characteristic directions at the sample level, is here about 5° lower than calculated for the directions obtained from Ksi¹¿ Wielkopolski IG-2 (Tab. 1). The middle parts of the Schilfsandstein and the Patoka Member were magnetized by the normal geomagnetic field (Fig. 6). The reversed-polarity record seems to be predominant in the lower parts of these units. Such a record is also displayed by single samples from the Ozimek Mem- ber (Upper Carnian).

Patoka 1 Most of the samples taken from the red beds of the Patoka Member contain two components of magnetization. A viscous component was removed at temperatures of up to 200 °C (Fig. 7). The sharp decrease of magnetization observed in some samples up to 150 °C probably reflects the presence of goethite (Fig. 7, sample P196-5A). The CHRM component was demagnetized at temperatures exceeding 600 °C (Fig. 7, samples P126C, P170B), indicating hematite as carrier. Some of the samples taken from the pink claystones were palaeomagneticaly unstable after a significant increase of magnetic susceptibility during heating (Fig. 7, samples P100C, P108C, P95-8B). This increase is probably due to transformation of ferric sulphides (at temp. ca. 350– 400 °C) and/or clay minerals (at temp. >600 °C) to magne-

plots of characteristic inclination and magnetic polarities are pre- Fig. 4. Lithostratigraphy of the Upper Triassic deposits in the sented. In the inclination plot, a single circle represents the charac- Ksi¹¿ Wielkopolski IG-2 core and the results of magnetostratigra- teristic direction isolated by the line-fit method from at least 2 phic investigations. On the right of the lithostratigraphic column, specimens. For lithologic symbols, see Fig. 1. MAGNETIC POLARITY OF UPPER TRIASSIC SEDIMENTS 669

tite (e.g., Dunlop and Özdemir, 1997). Single samples taken Longobardian boundary (Muttoni et al., 2000). The palaeo- from the red clays revealed the presence of well defined sta- magnetic data from the Schilfsanstein fits very well the up- ble magnetization carried by hematite, but with very steep per part of the Julian sub-stage that contains the same con- inclinations (Fig. 7, sample P60-8C). Such high values of chostracans (Kozur and Weems, 2010). The early Tuvalian inclination could indicate a secondary (Cenozoic) origin of part of the composite scale is not covered by magnetostra- the remanence. Very unstable palaeomagnetic directions ac- tigraphy. According to the correlation by the present au- companied with a huge increase in magnetic susceptibility thors, it should contain at least one normal-polarity zone were observed in the grey-coloured sediments. They did not that was recognized in the bottom part of the Upper Gyp- provide any reliable characteristic direction. Because of sumkeuper (equivalent to the Ozimek Member). The sup- this, the composite magnetic-polarity scale constructed for posed Early Norian part of this record with two distinct nor- this core is very limited (Fig. 8). However, one can con- mal-polarity zones can be correlated with the coeval polar- clude that normal-polarity palaeomagnetic behaviour seems ity pattern, documented so far in the Newark Basin and S to be predominant in the Patoka Member, which was depos- Europe (Gradstein et al., 2012). However, the uppermost ited during the Norian (see Œrodoñ et al., 2014; Fija³- part of the Ozimek Member and the lowermost part of the kowska-Mader et al., 2015; Szulc et al., 2015). Only single Patoka Member containing a reversed-polarity record, are samples from the bottom and top parts of the section studied most probably still of latest Tuvalian age (~228.5 Ma). An- revealed the presence of a reversed-polarity record. How- other possibility is to correlate them with the middle Lacian ever, two of these samples have a very steep inclination (~224.5 Ma) (Fig. 10). However, if the “Long-Tuvalian” (~80°) with a characteristic component distant from the mean option of the Late Triassic Time Scale (see above) is taken inclination, calculated for the rest of samples (Tab. 1), and into consideration, the parts of these substages mentioned because of this their reversed polarity cannot be of primary should be correlated with ~221.5 Ma and ~218.5 Ma respec- Triassic origin. tively. The well-defined magnetozone URr1of reversed polarity in the top part of the Rhaetian can be correlated with the same polarity magnetozone SA5n, 1r was recognized in a MAGNETOSTRATIGRAPHIC similar position in St. Audrie’s Bay (Hounslow et al., 2004) CORRELATION or with the top part of the magnetozone E22 in the sequence of the Newark Basin (Kent and Olsen, 1999). This second so- Magnetozones covering relatively continuous frag- lution implies that time-equivalents of the youngest Triassic ments from the WoŸniki K1 and Ksi¹¿ Wielkopolski IG-2 rocks from the St. Audrie’s Bay, i.e. the Lilstock Formation cores were numbered (Fig. 9). Integration of magnetostrati- could not occur in the Ksi¹¿ Wielkopolski IG-2 core. graphic results from both cores allowed the recognition of 22 numbered magnetozones, which correspond to about 25% of the magnetozones distinguished in the Upper Trias- CONCLUSIONS sic of the Newark Basin or S Europe only (see Hounslow and Muttoni, 2010). The magnetozones defined in this pa- 1. Some of the Upper Triassic samples from the Ger- per cover not more than a third of the entire Upper Triassic man Basin in Poland revealed a good palaeomagnetic signal succession of the Germanic Basin in Poland. The mag- and provided characteristic directions of mixed polarity and netic-polarity pattern, reconstructed for the Schilfsanstein inclinations, corresponding to those expected for that time (magnetozones SCHr1 to SCHr3) and the Lower Norian interval. sediments (magnetozones NRr1 to NRn3) from the Ksi¹¿ 2. A total of 22 magnetozones were distinguished and Wielkopolski IG-2 core, is a good fit for the magnetozones named in the rocks studied. They account for about 25% of defined in the coeval rocks of the WoŸniki K1 core. The magnetozones that were found in the Upper Triassic rocks predominantly normal-polarity record obtained in the Pa- of the Newark Basin, S Europe and Turkey and were used toka 1 core most probably in part corresponds to the magne- for the construction of the composite Late Triassic Polarity- tozones NRn2 and NRn3, distinguished in the Ksi¹¿ Wiel- Time Scale. kopolski IG-2 and WoŸniki K1 cores (compare chemostra- 3. The magnetic-polarity pattern defined for the Schilf- tigraphic correlation of the Patoka 1 and WoŸniki K1 sec- sanstein and the lower Grabowa Formation is almost the tions in Œrodoñ et al., 2014, fig. 19; see also Szulc et al., same in cores from the Ksi¹¿ Wielkopolski IG-1 and WoŸ- 2015). niki K-1 boreholes. The predominantly normal polarity re- The magnetostratigraphic scale compiled for the Ger- cord defined for the Patoka 1 core corresponds most proba- manic Basin in Poland was compared with the composite bly in part to the Early Norian magnetozones NRn2 and Late Triassic polarity-time scale, constructed against the NRn3 specified in those cores. background of the data obtained from coeval rocks in N 4. The Schilfsanstein mixed magnetic polarity pattern America, S Europe, the United Kingdom and Turkey (see corresponds very closely to the one recognized in the upper above), and the age was calibrated according to the “long- part of the Julian sub-stage of the Tethys area. Rhaetian” option (Gradstein et al., 2012). In this solution, the base of the Rhaetian is defined at 209.5 Ma and the base of the Norian is calibrated at 228.4 Ma (Fig. 10). The Lower Acknowledgments Keuper part of the record in Poland fits well to the polarity We are greatly indebted to two anonymous reviewers for their zones distinguished in S Europe, close to the Fassanian and insightful comments on the manuscript. This work was partly sup- 670 J. NAWROCKI ET AL.

Fig. 5. Lithostratigraphy of the Upper Triassic deposits in the WoŸniki K1 core and the results of magnetostratigraphic investigation of them. On the right of the lithostratigraphic column, the plots of characteristic inclinations and magnetic polarities are presented. In the inclination plot, the larger circle represents the characteristic direction, isolated by the line-fit method from at least 2 specimens. The smaller circle indicates the characteristic direction, isolated from one specimen only. For lithologic symbols, see Fig. 1.

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Fig. 6. Typical demagnetization characteristics (demagnetization paths, intensity decay curves, orthogonal plots and changes of magnetic susceptibility) of’ the Upper Triassic samples from the Patoka 1 core. Open circles in the orthogonal plots represent vertical projections, full circles represent horizontal projections. M – intensity of remanent magnetization, Mmax – initial intensity of natural remanent magnetization. The diagrams were prepared by the means of a computer package, written by Chadima and Hrouda (2006). MAGNETIC POLARITY OF UPPER TRIASSIC SEDIMENTS 671 672 J. NAWROCKI ET AL.

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Fig. 8. Magnetic stratigraphy and correlation chart of the Upper Triassic sequences from the Ksi¹¿ Wielkopolski IG-2, WoŸniki K1 and Patoka 1 cores. For lithologic symbols, see Fig. 1.

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Fig. 9. Correlation of polarity pattern obtained in this study with the composite Late Triassic polarity-time scale, prepared according to a “Long-Rhaetian” option of stratigraphy (see Gradstein et al., 2012, p. 709). Position of Conchostracan zone with Schilfsandstein fauna, according to Kozur and Weems (2010).

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